Have you already studied to your heart's content the touristy attractions of Drupal 7 (Entity API, Fields, AJAX framework, etc.)? Looking to see something unexpected in Drupal 7? You're in luck.
Visit with me the semi-secret neighborhoods of Drupal 7, only known by some natives.
* Queues and Jobs: execute long-running jobs easily and reliably
* Pluggeable caches: do you love Cache Router, but hope it was properly maintained?
* Extensible database drivers: ever wanted to be able to alter the behavior of the database engine, to optimize your cluster?
* Stream wrappers: store your files in a scalable way
* Intelligent session handler and external cache: serve 100% of your anonymous pages from cache
* And even more.